Focus: point beneath earth's surface where rock that's under stress breaks, causing an earthquake Epicenter: point on the surface directly above the focus Seismic Waves: vibrations that travel through earth carrying the energy released during an earthquake P Waves: earthquake waves that compress and expand the ground like an accordian S Waves: earthquake waves that vibrate from side to side and up and down Surface Waves : move slower than P and S waves, but they make the most severe ground movements Seismograph: records ground movements caused by seismic waves as they move through earth Mercalli Scale: developed to rate earthquakes according to their intensity Richter Scale: rates the size of seismic waves as measured by a particular type of mechanical seismograph Moment Magnitude Scale: rating system that estimates the total energy released by an earthquake
Outline
Seismic Waves
three types of seismic waves
Primary waves (P waves)
earthquake waves that compress and expand ground
Secondary waves (S waves)
earthquake waves that vibrate from side to side and up and down
surface waves
move slower that P and S waves but produces the most severe ground movements
Detecting Seismic Waves
seismograph records ground movements caused by seismic waves
electronic seismograph converts ground movements into a signal that can be recorded or printed
Measuring Earthquakes
magnitude measures earthquake strength based on seismic waves and movement along faults
mercalli scale
rates earthquakes according to their intensity
developed in twentieth century
earthquakes's intensity is the strength of its ground motion in a chosen place
richter scale
rates the size of seismic waves measured by a particular type of mechanical seismograph
developed in 1930s
accurate for nearby or small earthquakes
isn't very accurate if earthquake is far or large
moment magnitude scale
used to rate earthquakes of all sizes
Locating the Epicenter
geologists locate an earthquake's epicenter using seismic waves
seismic waves travel at different speeds
P waves arrive before S waves
scientists measure the difference between the arrival time of P and S waves to find out how far the epicenter is from the seismograph
the greater the time difference is with P and S waves, the farther away an earthquake is
geologists draw at least three circles using data from seismographs
center of each circle is a particular seismograph's location
radius of each circle is the distance from the seismograph to the epicenter
point where the three circles intersect is the location of the epicenter
Table of Contents
2.2 Measuring Earthquakes
Vocabulary
Focus: point beneath earth's surface where rock that's under stress breaks, causing an earthquake
Epicenter: point on the surface directly above the focus
Seismic Waves: vibrations that travel through earth carrying the energy released during an earthquake
P Waves: earthquake waves that compress and expand the ground like an accordian
S Waves: earthquake waves that vibrate from side to side and up and down
Surface Waves : move slower than P and S waves, but they make the most severe ground movements
Seismograph: records ground movements caused by seismic waves as they move through earth
Mercalli Scale: developed to rate earthquakes according to their intensity
Richter Scale: rates the size of seismic waves as measured by a particular type of mechanical seismograph
Moment Magnitude Scale: rating system that estimates the total energy released by an earthquake
Outline
Seismic Waves
Detecting Seismic Waves
Measuring Earthquakes
Locating the Epicenter
Diagram